Unit 20: The Reproductive System and Human Development
How a body produces the next generation, from sperm and egg to a fully developed fetus ready to be born.
4 topics · 12 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Male Reproductive System
- How it worksHow do the testes produce sperm cells and the hormone testosterone?
- Common mistakeWhy doesn't sperm production happen at a constant unchanging rate throughout a man's life?
- Ties togetherHow does the male reproductive system's hormone signaling connect to the negative feedback loops covered earlier?
Your turn1 of 2
The testes sit inside the scrotum, outside the main body cavity, keeping them a few degrees cooler than core body temperature. Why does sperm production require a slightly cooler temperature than the rest of the body?The Female Reproductive System and the Menstrual Cycle
- How it worksWalk me through how rising and falling hormone levels drive the phases of the menstrual cycle.
- Worked exampleFind approximately which day of a 28-day menstrual cycle ovulation occurs.
- Common mistakeWhy isn't menstruation itself the release of an egg from the ovary?
Your turn1 of 2
In a menstrual cycle lasting 32 days total, ovulation typically occurs about 14 days before the next period begins, meaning on approximately day (c minus 14) of the cycle. On approximately which day of this 32-day cycle does ovulation occur?Fertilization and Early Development
- How it worksHow does a fertilized egg divide repeatedly to form a hollow ball of cells before implanting in the uterus?
- Common mistakeWhy doesn't fertilization happen inside the uterus rather than in the fallopian tube?
- Going furtherWhat happens to a fertilized egg's genetic material compared to the separate egg and sperm cells that combined?
Your turn1 of 2
A single ejaculation releases tens of millions of sperm cells, yet typically only one of them ends up successfully fertilizing an egg. Why does only one sperm cell out of millions typically end up fertilizing an egg?Pregnancy and Fetal Development
- How it worksHow does the placenta exchange nutrients, oxygen, and waste between mother and fetus without mixing their blood?
- How it worksHow do the three trimesters of pregnancy mark distinct stages of organ formation and growth?
- Common mistakeWhy doesn't a mother's blood flow directly into her developing baby's circulatory system?
Your turn1 of 2
A developing fetus depends entirely on its mother for nutrients and oxygen, yet the fetus doesn't drink or eat directly from its mother's own bloodstream. Why does a developing fetus need a placenta instead of feeding directly from its mother's bloodstream?